British scientists have confirmed that one of the rarest meteorites ever to fall to Earth is from a time when the Solar System was born.

It provides a glimpse of a period, 4.5 billion years ago, when the planets were just beginning to form.

It's unlike any other meteorite we've ever seen so it possibly belongs in a group all of its own

Emma Bullock, Natural History Museum

The meteorite has a composition that is quite unlike Earth rocks and one that is distinct from all other space rocks so far recovered. It may even belong in a meteorite class of its own, say researchers at London's Natural History Museum.

A team led by Dr Sara Russell is one of a handful around the world that is analysing slivers of the rock.

It came down over Tagish Lake, a remote area of northern Canada, on 18 January, 2000.

Fragments landed on a frozen lake and were preserved in ice almost immediately.

By a stroke of luck, they were found by someone who knew to keep them cold and not to touch them.

"It turns out that this meteorite is a really unique sample," says Dr Russell. "It's higher in extra-terrestrial organic material than any other meteorite."

Building blocks

Research at the museum has confirmed that the Tagish meteorite is "extremely primitive" in its chemical composition.

It has changed little since it first arose "in the very earliest stages of the Solar System," says Dr Russell.

Tiny grains in the rock should reveal new information about the dust and gases that came together to make the planets.

"Our work on Tagish lake is very much work in progress at the moment," Dr Russell told BBC News Online. "What we think we've found is that this is a sample of the very earliest building blocks of the materials that went on to make up the planets in our Solar System."

The sample gives scientists a chance to learn more about how the planets formed.

It could also reveal whether or not other Earth-like planets are likely to be found around other young stars.